This is the free version.
PaceCalc pro (which is also available at the AppStore) allows individual configuration of Your distances in miles and km. With buying PaceCalc pro you support my work.
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PaceCalc allows easy calculation of the pace (min/km or min/mile) or the total time of your runs.
Select a distance: Marathon (M), Half-Marathon (HM), 35km/miles (35), 25km/miles (25), 15km/miles (15) or 10km/miles (10) and enter your total time or your pace and the pace or the total time will be calculated.

Replying to a review in the US Store: Yes it is in min/mile as well - just toggle the mode (min/km min/mile) via the small button right below the calculated time or by tapping on the mode-text in the middle of the toolbar at the bottom. See screenshots for different modes.
...My documentation should have been better ;-)